1. Field of the Invention
The present invention relates to the chemical-mechanical polishing (CMP) process used in the manufacturing of semiconductor devices. More particularly, the present invention relates to the pad conditioner head of a CMP machine.
2. Description of the Related Art
In the fabrication of integrated circuits of a semiconductor device, a chemical-mechanical polishing (CMP) process is generally used to reduce step coverage, or to form contact plugs and wires in a damascene manner. To this end, the CMP process uses mechanical friction and a chemical reaction to remove material from the surface of a wafer. In the CMP process, a polishing head presses a wafer against an abrasive pad and rotates the wafer, whereby the wafer is mechanically polished. Also, during this time, a slurry arm supplies a slurry of abrasive particles into a small gap between the wafer and the abrasive pad to chemically remove silicon oxides from the wafer. CMP is very efficient in removing material from the surface of a wafer because CMP makes use of both mechanical and chemical processes. Also, the use of a chemical reaction allows for only selected material to be removed from the surface of a wafer.
However, a precise surface roughness and elasticity of the abrasive pad and a specified contact pressure between the wafer and the abrasive pad have to be established if the CMP process is to remove material precisely from the surface of a wafer. Also, the slurry has to be uniformly distributed in the gap between the surface of the wafer and the abrasive pad. Accordingly, the abrasive pad is precisely fabricated to satisfy these requirements. If, however, the characteristics of the abrasive pad change significantly after the pad has been used for a given period of time, it has to be replaced. Moreover, the abrasive pad is an expensive consumable article of manufacture. Therefore, its frequent replacing has a noticeable impact on the manufacturing cost of the semiconductor devices.
Accordingly, the abrasive pad needs to be maintained for a long period of time. To meet this need, a pad conditioner is used to condition the surface of the abrasive pad so that the surface remains uniform for as long as possible. The pad conditioner evens out irregularities in the surface contour of the abrasive pad and remove surplus slurry from the surface of the abrasive pad so that the slurry is distributed uniformly across the surface of the abrasive pad. The pad conditioner also trims the surface of the abrasive pad so that a given surface roughness is maintained. Thus, the pad conditioner prolongs the useful life of the abrasive pad and maintains the condition of the pad until its useful life is over.
FIG. 1 is a schematic plan view of a conventional CMP machine. The CMP machine has several working area P1, P2, P3. A respective abrasive pad 11, a slurry arm 13, and a pad conditioner 15 having a head 21 are disposed in each working area. The abrasive pad 11 is mounted on a circular platen (23 of FIG. 3). The slurry arm 13 and the pad conditioner 15 are disposed in a first corner of the working area. On the other hand, a respective polishing head 19 is disposed over the abrasive pad 11 at a second corner of each working area opposite to that corner at which the slurry arm 13 and the pad conditioner 15 are disposed. The polishing head 19 chucks a wafer 17 by vacuum or surface tension during the CMP process in which, as mentioned above, the wafer 17 is pressed by the polishing head against the abrasive pad 11 while the abrasive pad 11 is rotated (by the platen 23) and the slurry arm 13 supplies slurry into the gap between the contacting surfaces of the wafer 17 and the abrasive pad 11.
Subsequently, the head 21 of the pad conditioner 15 is moved onto the abrasive pad 11 from a stand-by position in a clean cup. The head 21 has a diamond-encrusted disk mounted thereto. The head 21 evens out the surface of the abrasive pad 11 by sweeping the disk across the pad 11 over a certain angle, whereby the centers of the platen 23 and the head 21 of the pad conditioner 15 are moved within a certain range relative to each other.
To maintain a sufficient surface roughness of the abrasive pad 11, the head 21 of the pad conditioner 15 has to be swung to the left and right within a given working range. If the movement of the pad conditioner 15 deviates from the given working range, excess slurry can remain on a portion of the abrasive pad 11, or steps or defective abrasive portions can be formed on the surface of the abrasive pad 11. Steps at the surface of the abrasive pad 11 may cause the wafer to be improperly polished. As a result, chips of inferior quality may be produced at a portion of the wafer 17.
Therefore, in preparation for the CMP process, the pad conditioner 15 is first adjusted to limit its movement within the desired given working range, however, components of the CMP machine may be mechanically altered as the CMP process is being carried out. Accordingly, it is necessary to frequently calibrate the head 21 of the pad conditioner 21, i.e., set the head 21 in place in a reference position.
Referring to FIG. 2 and FIG. 3, the head 21 is so calibrated by vertically aligning the outer peripheral edge thereof with the outer peripheral edge of the platen 23. Up until now, the pad conditioner head 21 has been calibrated in this way by eye. However, it is not possible to accurately calibrate the head 21 consistently and correctly by eye. In particular, it is very difficult to discern whether the edge of the head 21 is vertically aligned with the edge of the platen 23 because the abrasive pad 11 protrudes outwardly beyond the edge of the platen 23.
Accordingly, the head 21 is often improperly calibrated, whereby the pad conditioner 15 operates outside the desired working range when conditioning the abrasive pad. As a result, excess slurry can be remain on a portion of the abrasive pad 11, or steps or defective abrasive portions can be formed on the surface of the abrasive pad 11. As a result, inferior chips are often produced.
It is an object of the present invention to provide a device by which a pad conditioner head of a CMP machine can be correctly calibrated, especially in the case in which the abrasive pad of the CMP machine protrudes radially outwardly beyond an outer peripheral edge of the circular platen to which the pad is mounted.
The present invention achieves this abject by providing by a calibration device that includes a first horizontal member having a radially innermost end defining a concave arcuate reference surface having a shape complementary to that of a portion of the outer peripheral edge of the platen, a second horizontal member extending radially relative to the concave arcuate reference surface of the first horizontal member and bearing a reference mark located in the projected plane of the reference surface, and a connecting member interconnecting and vertically spacing the first and second horizontal members.
The innermost end of the first horizontal member is elongate relative to the outermost end thereof, in the circumferential direction of the platen, so that the reference surface can engage the outer peripheral edge of the platen over a rather wide area. Furthermore, when the calibration device is in use, the outermost end of the first horizontal member and an outermost end of the second horizontal member opposite thereto are located further out than a portion of the outer peripheral edge of the abrasive pad that extended outwardly beyond the outer peripheral edge of the platen. Thus, the abrasive pad can be accommodated in a space between the horizontal members of the calibration device.
The connecting member can be unitary with the first and second horizontal members. In addition, a handle can be integrated with the connecting member so that the calibration device can be grasped.
The reference mark can be part of a scale formed on the second horizontal member. Also, the calibration device may include a scale extension disposed on the second member so as to be movable along the scale relative to the reference mark. The scale extension projects laterally from the second horizontal member in an arc having a curvature similar to (meaning the same or nearly the same as) that of the outer peripheral edge of the platen.
When the reference surface of the first horizontal member of the calibration device is butted against a portion of the outer peripheral edge of the platen adjacent the head of the pad conditioner, the location of the outermost portion of the head of the pad conditioner relative to the reference mark is readily observable. Thus, the extent to which the outermost portion of the head of the pad conditioner is vertically aligned relative to the outer peripheral edge of the platen can be easily and accurately determined, whereby the pad conditioner can be, in turn, accurately calibrated.